Modified asphalt compositions

ABSTRACT

A modified asphalt composition is provided comprising at least one plastomer, at least one elastomer, and asphalt. More specifically, a modified asphalt composition is provided comprising an oxidized polyethylene, a styrene-butadiene-styrene block copolymer, and asphalt. A hot mix asphalt composition is also provided comprising the modified asphalt composition and aggregate. Processes for producing the modified asphalt composition and the hot mix asphalt composition is also provided as well as articles produced from these inventive compositions.

This is a reissue of Ser. No. 10/706,454, now U.S. Pat. No. 7,144,933,filed Nov. 12, 2003.

JOINT RESEARCH AGREEMENT

The names of the parties to the joint research agreement are EastmanChemical Company and PRI Asphalt Technologies, Inc.

FIELD OF THE INVENTION

The present invention relates to modified asphalt compositionscomprising at least one plastomer, at least one elastomer, and asphalt;wherein the elastomer is optionally crosslinked with at least onecrosslinking agent. More particularly, the present invention is directedto modified asphalt compositions for use in road pavement. The presentinvention also relates to hot mix asphalt compositions comprising atleast one plastomer, at least one elastomer, asphalt, and aggregate;wherein the elastomer is optionally crosslinked with at least onecrosslinking agent.

BACKGROUND OF THE INVENTION

Asphalt is a commonly used material for construction purposes, such as aroad pavement or roofing material. Asphalt alone, however, often doesnot possess all the physical characteristics desirable for manyconstruction purposes. For instance, unmodified asphalt may exhibit apoor Performance Grade Rating (PG Rating) as a road pavement material.As used herein, PG Rating is defined as the average seven-day maximumand the single-day minimum pavement design temperature, wherein themaximum is determined 20 mm below the surface of the pavement and theminimum is determined at the surface of the pavement. Although the PGRating for asphalt may widely vary, asphalt generally used in roadpavement applications exhibit PG Ratings of about 64-22, which indicatesa 64° C. average seven day maximum and a −22° C. single day minimumpavement design temperature.

When used as a road pavement material, asphalt is typically subjected totemperatures in excess of 64° C. twenty mm below the pavement surfaceand below −22° C. at the pavement surface. Temperatures outside thisrange lead to deterioration of the asphalt. pavement. Hence, it has forsome time been an objective to broaden the PG Rating range of asphaltused in road pavement applications.

To broaden the PG Rating range of the asphalt pavement, modifiers areadded to the asphalt. In addition to increasing the PG Rating range ofthe asphalt, modifiers also can improve other qualities of the asphalt,such as its toughness, flexibility and wear characteristics. Typically,modifiers are added to molten asphalt and mixed for several hours toproduce a modified asphalt. Then, crosslinking agents can be added. Themodified asphalt is then routed to a mixer where aggregate is added toproduce the hot mix asphalt (HMA). The hot mix asphalt is then taken tothe construction site for use in paving equipment.

Three major problems associated with the performance of hot mix asphalts(HMA) pavements can be moisture susceptibility (stripping), permanentdeformation (rutting, bleeding and shoving) and cracking (thermal andfatigue). There are a number of modifiers that can be added to the HMAmixture that can provide a solution to each of these problemsindividually. Liquid anti-strips and hydrated lime are additives thatcan be used to reduce moisture susceptibility problems. They alter thesurface chemistry at the interface between the aggregate and the asphaltresulting in an improved bonding of the asphalt and aggregate. Polymerscan be used to modify an asphalt to increase the high temperaturestiffness of the HMA, which can reduce the probability of rutting,bleeding and shoving. Polymers may be selected and used to impartelastomeric properties which can reduce thermal and fatigue cracking byallowing the modified asphalt to undergo repeated strains with recovery.However, it is difficult to find a modifier that will provide a solutionto these problems simultaneously especially one that does not requirehigh shear blending or modified blending procedures.

The current methods used in the United States to make an asphalt hot mixfor road paving involves melting the asphalt in a large heated tank andadding 2 to 6 percent of an elastomer. Typically, high dosages ofelastomer are used globally, usually a synthetic rubber such as styrenebutadiene styrene block copolymer (SBS). The SBS block copolymerdissolves slowly in the asphalt due to viscosity differences when onlystirring is used. Tanks equipped with high shear stirrers shorten thetime to dissolve the elastomer. After the elastomer is dissolved acrosslinking agent, such as sulfur, peroxide or a transition metal canbe added to crosslink the elastomer. Adding the cross-linking agent,sulfur, at the same time as the SBS block copolymer results in immediateand localized cross-linking, which may manifest itself as agglomeratedSBS clumps that do not dissolve quickly or easily. These clumps canrequire further blending/milling. The SBS block copolymer can actuallyform a matrix in the asphalt. If the crosslinking agent is added toosoon to the mix, before the rubber has dissolved, an intractable mass ofrubber is formed which is not dissolvable. If the crosslinking agent isadded late, both time and money are then wasted. Hence, the addition ofthe crosslinking agent is critical to the correct make up and economicsof the asphalt hot mix.

The use of sulfur to crosslink rubber has been known in the industry forabout a hundred years. Much research has been concerned with adjustingthe speed of the crosslinking reaction. That is, the development ofaccelerators, crosslink modifiers and retarders has been a verylucrative and fruitful area of research for the many chemical suppliersto the vulcanization industry. However, it should be noted that allmodifications to the timing of sulfur as a crosslinking agent haveresulted in shorter times to affect more crosslinking. Thus, no additiveis available to prolong, delay or slow down the action of the sulfurcrosslinking. Sulfur by itself is as slow as sulfur can be made tocrosslink at a given temperature.

Cross-linking of the hot asphalt mix is not required, but highlypreferred. Without cross-linking, more elastomer and elastomer of highermolecular weight are required to achieve the same end point, adding costto the modification package. The use of a cross-linking agents permitsthe use of lower molecular weight elastomers, which are inherentlyeasier to dissolve and may be lower cost. Sulfur, if used, is actually acost reducer since it allows less elastomer to be used to achieve thesame performance properties.

The addition of the elastomer to the tank of asphalt usually involvesdumping a large quantity of elastomer into the top of the mix tank. Whenthe sulfur is added similarly, a large disagreeable cloud of dust can beformed as well as fumes from the sulfur contacting the molten asphalt.In some cases, a hazardous sulfur cloud or sulfur gases can form andresulting odor may lead to the evacuation of the area until the cloudsubsides. Even the addition of chunks of sulfur can lead to dust cloudsand disagreeable odor.

The process of introducing finely divided dry materials, such as sulfur,into hot reaction vessels or tanks can present a hazard due to theformation and presence of sulfur dioxide or hydrogen sulfide vapors incombination with elevated processing temperatures. In addition, finelydivided dry materials often do not mix efficiently when combined withthe liquid material in the system. In an attempt to remedy this problem,the finely divided dry material can be pre-dispersed in oil. However,the tendency for the heavier finely divided material to settle requiresconstant agitation. More viscous oils and/or asphalt fluxes have beenutilized to prevent the settlement of the finely divided material, butthe use of these materials can require the application of higherprocessing temperatures to maintain the oil and or asphalt fluxes at apumpable viscosity. In addition, this method can also require constantagitation to maintain dispersion of the finely divided material. As aresult, the higher temperature needed in processing can increase therisks of emission of toxic gases, such as hydrogen sulfide, which ishighly toxic and flammable.

Elastomers are more difficult to disperse in molten asphalt. Theyrequire the use of high shear mixing, increased processing temperatures,and long mixing times to obtain a good mix. Elastomers tend to increasethe process viscosity of the asphalt. This increase in process viscositycan make the modified asphalts more difficult to mix and coat theaggregate in the mixing zone and subsequently more difficult to compactduring installation of the hot mix asphalt composition. This is atechnical and practical issue currently occurring in the industry.Typically, elastomers commonly used do not improve adhesion to aggregatein wet environments and can contribute to anti-stripping properties.These hot mix asphalt compositions still require the inclusion of ananti-stripping additive.

It is, therefore, apparent that there is a need for asphalt modifierscapable of modifying the physical characteristics of asphalt, asindicated by a broader PG rating. In addition, there is a need formodified asphalt compositions where the modifiers are easily dispersedin the asphalt. Furthermore, there is a need for modified asphaltcompositions where there is reduction in dust and gas formation when themodifiers are added to the molten asphalt.

SUMMARY OF THE INVENTION

Surprisingly, the inventors have found modified asphalt compositionshaving at least one of the following improvements: broader PG rating,reduction in gas and dust formation upon addition of modifiers, improvedease of dispersion of the modifiers in the molten asphalt, and long-termstorage stability and good workability.

In accordance with one embodiment of the invention, a modified asphaltcomposition is provided comprising at least one plastomer, at least oneelastomer, and asphalt, wherein the elastomer is optionally crosslinkedwith at least one crosslinking agent. The asphalt composition can beused for various purposes including paving and roofing. It isparticularly well suited for road paving applications.

In accordance with another embodiment of the invention, a hot mixasphalt composition is provided comprising at least one plastomer, atleast one elastomer, asphalt, aggregate, and wherein the elastomer isoptionally crosslinked with at least one crosslinking agent.

In accordance with another embodiment of the invention, a pellet isprovided comprising at least one elastomer and at least one plastomer;wherein the pellet is used as an asphalt modifier.

In accordance with another embodiment of the invention, a pellet isprovided comprising at least one plastomer and at least one crosslinkingagent; wherein the pellet is used as an asphalt modifier.

In accordance with another embodiment of the invention, an articleformed from the modified asphalt composition or the hot mix asphaltcomposition is provided. In a preferred embodiment of the presentinvention, the article formed from the modified asphalt composition orhot mix asphalt composition is road pavement.

In accordance with yet another embodiment of the invention, a process toproduce the modified asphalt composition is provided. The processcomprises contacting at least one plastomer, at least one elastomer,asphalt, and optionally at least one crosslinking agent to produce themodified asphalt composition.

In accordance with still another embodiment of the invention, a processto produce a hot mix asphalt composition is provided. The processcomprises contacting at least one plastomer, at least one elastomer,asphalt, aggregate, and optionally at least one crosslinking agent toproduce the hot mix asphalt composition.

These and other features, and advantages of the present invention willbecome more fully apparent from the following description and appendedclaims, or may be learned by the practice of the of the invention as setforth hereinafter.

DETAILED DESCRIPTION OF THE INVENTION

It must be noted that, as used in the specification and the appendedclaims, the singular forms “a,” “an” and “the” include plural referentsunless the context clearly dictates otherwise. Thus, for example,reference to “an asphalt” includes mixtures of two or more suchasphalts, and the like.

Ranges are often expressed herein as from “about” one particular value,and/or to “about” another particular value. When such a range isexpressed, another embodiment includes from the one particular valuecontained in the range and/or to the other particular value contained inthe range. Similarly, when values are expressed as approximations, byuse of the antecedent “about,” it will be understood that the particularvalue contained in the range forms another embodiment.

The term “asphalt” is a dark brown to black cementitious material whichis solid or semi-solid in consistency, comprising bitumens as itspredominant constituent. Typically, asphalt is described as a blacksolid with a dull luster.

The term “thermal cracks” is defined as cracks resulting from internalstresses induced by temperature change and stresses exceeding thestrength of the pavement. Thermal cracks typically occur at lowtemperatures.

The term “rutting” is defined as a form of permanent deformation, whereshearing forces, such as from an automobile wheels push the asphaltlayers apart resulting in ruts. Rutting generally occurs at hightemperatures.

The term “fatigue cracking” is defined as crack patterns that can leadto potholes. Fatigue cracking generally occurs over a period of time andat low to moderate pavement temperatures.

It is a feature of the present invention to provide a modified asphaltcomposition comprising at least one plastomer, at least one elastomer,asphalt, and optionally wherein the elastomer is crosslinked with atleast one crosslinking agent.

It is further a feature of the present invention to provide a plastomerand elastomer that is compatible with asphalt and which is easilydispersed in asphalt without the use of expensive mixing equipment orprocesses.

The elastomer, plastomer, and optionally, the crosslinking agent can beadded to the asphalt in any amount necessary to obtain the propertiesdesired by the modified asphalt composition. The amounts of course willvary depending on the characteristics of the asphalt. Preferably, theamounts added increase the PG rating of the modified asphalt compositionby +1 to +3 grades.

The plastomer can be present in the modified asphalt mixture in anamount from about 0.1% by weight to about 10% by weight based on theweight of the modified asphalt composition, preferably from about 0.5%by weight to about 7% by weight, and most preferably 1% by weight to 5%by weight. The elastomer can be present in the modified asphaltcomposition in an amount from about 0.1% by weight to about 10% byweight based on the weight of the modified asphalt composition,preferably from about 0.5% by weight to about 7% by weight, and mostpreferably 1% by weight to 5% by weight. The crosslinking agent can bepresent in the modified asphalt composition in an amount from about 0.1%by weight to about 2% by weight based on the weight of the modifiedasphalt composition, preferably from about 0.5% by weight to about 2% byweight, and most preferably 0.5% to 1.5% by weight.

Alternatively, the plastomer and elastomer can be combined together toproduce a plastomer/elastomer mix and then added to the asphalt. Whenthis method is utilized, the plastomer is present in theplastomer/elastomer mix in an amount from about 0.1% by weight to 99.9%by weight, preferably from 25% by weight to 80% by weight based on thetotal weight of the plastomer and elastomer. The elastomer can bepresent in the plastomer/elastomer mix in an amount from about 0.1% byweight to 99.9% by weight, preferably from 25% by weight to 80% byweight based on the total weight of the plastomer and elastomer.Preferably, the plastomer and elastomer are extruded in an extrudingzone to produce plastomer/elastomer pellets, and the plastomer/elastomerpellets are then added to the asphalt. The extruding zone comprises atleast one extruder.

In another embodiment, the plastomer and the crosslinking agent areextruded in an extruding zone to produce plastomer/crosslinking agentpellets, and the plastomer/crosslinking agent pellets are then added tothe asphalt. The amount of crosslinking agent in theplastomer/crosslinking agent pellets range from about 0.1% by weight toabout 5% by weight, preferably 1% by weight to 3% by weight based on theweight of the elastomer.

The asphalt used in the present invention may be any asphalt known inthe art. Preferably, the asphalt utilized in this invention is any thatis conventionally used in road paving applications. Such asphalt may beobtained from different sources, such as naturally occurring asphalt,vacuum distillation residue, or hydrocarbon cracking residue. The use ofasphalt derived as a residue from vacuum distillation is preferred.Asphalt may be further described by using its penetration value (“PEN”),asphalt cement viscosity value (“AC”), or asphalt aged residue viscosity(“AR”). The measurement of PEN values is defined by ASTM D5. Asphalt, asused herein, can have a PEN value of from about 40 to about 300 dmm. Themeasurement of AC viscosity values is defined by ASTM D2171. Asphalt, asused herein, can have an AC value of from about 2.5 to about 40 hundredsof poises. The measurement of AR values is defined by ASTM D2171.Asphalt, as used herein, can have an AR value of from about 1,000 toabout 16,000 poises.

The asphalt used in the present invention may be unmodified or modifiedasphalt. In some applications, oxidized asphalt provides differentweather resistance and stability characteristics. The asphalt can beoxidized by any means known in the art, including mixing the asphaltwith air and heating to between about 179° C. and about 260° C. with orwithout a catalyst. When no catalyst is used, it typically takes betweenfour to six hours to oxidize the asphalt. With a catalyst, theprocessing time is shortened to between about two and about four hours.A preferred catalyst is ferric chloride (FeCl₃).

In a preferred embodiment, the asphalt is an AC-20 type asphalt, onecommonly known as West Texas Intermediate which is commerciallyavailable from Ashland (ASHLAND AC-20).

The plastomer used in the present invention is any plastomer known inthe art having a density from about 0.92 g/cm³ to about 1.1 g/cm³ at 25°C. as measured by ASTM D-1505. The plastomer can be at least onehomopolymer or a copolymer having at least one polar functional groupand having a density from about 0.92 to about 1.1 g/cm³ at 25° C. Theplastomer is preferably selected from oxidized polyolefins, maleatedpolyolefins and acrylic acid grafted polyolefins. More preferably, theplastomer is selected from maleated polyethylene, maleatedpolypropylene, oxidized polyethylene, acrylic acid grafted polyethylene,acrylic acid grafted polypropylene and mixtures and derivatives thereof.Most preferably, the plastomer is an oxidized polyethylene.

In one embodiment of the present invention, the plastomer can haveproperties in at least one of the following ranges: an acid number fromabout 0.1 to about 50 as measured by ASTM D-1386, a needle penetrationhardness less than about 50 dmm at 25° C. measured by ASTM D-1321, and aviscosity from about 1 to about 100,000 cP at 135° C., as measured byD-1824.

In a preferred embodiment, the plastomer is an oxidized polyethylenehomopolymer having at least one of the following properties: a densityfrom about 0.92 to about 1.1 g/cm³, a hardness less than about 1.5 dmmat 25° C., an acid number from about 5 to about 41, and a viscosity fromabout 800 to about 8,000 cP at 125° C. Suitable plastomers arecommercially available from Eastman Chemical Company under the tradenameEpolene.

The elastomer is any synthetic rubber compound known in the art.Generally, synthetic rubbers are produced from monomers obtained fromthe cracking and refining of petroleum. Suitable monomers for theproduction of synthetic rubbers include, but are not limited to,styrene, butadiene, carboxylated butadiene, isobutylene, isoprene,carboxylated isoprene, chloroprene, ethylene, propylene, acrylonitrile,and mixtures thereof.

In one embodiment, the elastomer is a block copolymer of at least oneconjugated diene and at least one monoalkenyl aromatic hydrocarbon. Thepreferred conjugated dienes are butadiene, isoprene, chloroprene,carboyxlated butadiene, and carboxylated isoprene. Most preferably, theconjugated diene is butadiene and isoprene. The preferred monoalkyenylaromatic hydrocarbon is styrene. Such block copolymers can have ageneral formula A-B-A or (A-B)_(n) X wherein each A block is amonoalkyenyl aromatic hydrocarbon polymer block, each B block is aconjugated diolefin polymer block, X is a coupling agent and n is aninteger from 2 to about 30. Such block copolymers can be linear or mayhave a radial or star configuration as well as being tapered. Blockcopolymers such as these are Well known and are described in U.S. Pat.Nos. 4,145,298; 4,238,202; and 5,039,755; all of which are incorporatedby reference. The block copolymers can have a number average molecularweight from about 30,000 to about 300,000, as measured by ASTM D-5296.

When the conjugated diene is butadiene and the monoalkyenyl aromatichydrocarbon is styrene, the amount of styrene repeating units rangesfrom about 15% by weight to about 50% by weight based on the weight ofthe block copolymer, preferably from about 17% by-weight to 35% byweight, most preferably from 20% by weight to 31% by weight with theremainder being repeating units derived from butadiene.Styrene-butadiene block copolymers can have a number average molecularweight ranging from about 50,000 to about 200,000, preferably from80,000 to 180,000.

The block copolymer can employ a minimal amount of hydrocarbon solventin order to facilitate handling. Examples of suitable solvents includeplasticizer solvent that is a non-volatile aromatic oil.

In another embodiment of this invention, a modified asphalt compositionis provided comprising at least one plastomer, at least one elastomer,and asphalt, wherein the elastomer is crosslinked with at least onecrosslinking agent.

The crosslinking agent can be any that is known in the art capable ofcrosslinking with the elastomer. For example, crosslinking agents forasphalt are disclosed in U.S. Pat. Nos. 5,017,230; 5,756,565, 5,795,929,and 5,605,946; all of which are hereby incorporated by reference.

In one embodiment of the present invention, the crosslinking agent is atleast one selected from elemental sulfur, hydrocarbyl polysulfides,peroxides, and transition metals. The elemental sulfur capable of beingemployed to constitute, partially or wholly, the crosslinking agent canbe flowers of sulfur and sulfur crystallized in the orthorhombic form,known by the name of alpha sulfur.

The hydrocarbyl polysulfides capable of being employed to form at leasta portion of the crosslinking agent correspond to the general formula:R₁—(S)_(v)—[R₃—(S_(v))_(w)]—R₂wherein each of R₁ and R₂ denotes a saturated or unsaturated, monovalentC₁-C₂₀ hydrocarbon radical or R₁ and R₂ are joined together to form asaturated or unsaturated, divalent C₂-C₂₀ hydrocarbon radical forming aring with the other groups of atoms which are associated in the formula.R₃ is a saturated or unsaturated, divalent C₁-C₂₀ hydrocarbon radical.The —(S)_(v)—groups denote divalent groups each made up of v sulfuratoms. It is possible that the number of sulfur atoms, v, for each ofthese groups can differ. The number of sulfur atoms, v, denote integersranging from about 1 to about 6. Preferably, at least one of the—(S)_(v)— groups has at least two or greater sulfur atoms. In the group—[R₃—(S_(v))_(w)]—, w denotes an integer having values from 0 to about10.

In the abovementioned formula, the monovalent C₁-C₂₀ hydrocarbonradicals, R₁ and R₂ and the divalent C₁-C₂₀ hydrocarbon radical, R₃, arechosen especially from aliphatic, alicyclic, or aromatic radicals. Whenthe radicals R₁ and R₂ are joined together to constitute a divalentC₁-C₂₀ hydrocarbon radical forming a ring with the other groups of atomsassociated in the formula, the divalent radical can be similar to theradical R₃ and may also be of the aliphatic, alicyclic or aromatic type.Preferably, R₁ and R₂ are identical and chosen from C₁ to C₂₀ alkylradicals, such as, but not limited to, ethyl, propyl, hexyl, octyl,nonyl, decyl, linear dodecyl, tert-dodecyl, hexadecyl, octadecyl, andC₆-C₂₀ cycloalkene or arylene radicals, expecially phenylene, toluene,and cyclohexene.

Examples of polysulfides include, but are not limited to, dihexyldisulfide, dioctyl disulfide, didodecyl disulfide, di-tert-dodecyldisulfide, dihexadecyl disulfide, dihexyl trisulfide, dioctyltrisulfide, dinonyl trisulfide, di-tert-dodecyl trisulfide, dinonyltrisulfide, di-tert-dodecyl trisulfide, dihexadecyl trisulfide, dihexyltetrasulfide, dioctyl tetrasulfide, dihexadecyl tetrasulfide, dioctyltetrasulfide, dinonyl tetrasulfide, di-tert-dodecyl tetrasulfide,dihexadecyl tetrasulfide, dihexyl pentasulfide, dioctyl pentasulfide,dinonyl pentasulfide, di-tert-dodecyl pentasulfide, dihexadecylpentasulfide, diphenyl trisulfide, dibenzyl trisulfide, diphenyltetrasulfide, ortho-tolyl tetrasulfide, dibenzyl tetrasulfide, dibenzylpentasulfide, diallyl pentasulfide, tetramethyltetrathiane, and mixturesthereof.

Any peroxide known in the art capable of crosslinking with the elastomerof this invention can be utilized. Examples of such peroxides include,but are not limited to, hydroperoxides, dialkyl peroxides,peroxydicarbonates, diacyl peroxides, peroxyesters, and others.

Any transition metal compound known in the art capable of crosslinkingwith the elastomer of this invention can be utilized. Examples of suchtransition metal compounds include, but are not limited to, zinccompounds, such as, zinc oxide; nickel compounds, such as nickel(II)chloride; and titanium compounds, such as, titanium halides and titaniumhydroxides. Other active metal compounds known to react withunsaturation can be used.

Although not necessary in this invention, if desired, crosslinkingaccelerators can be utilized. Crosslinking accelerators are disclosed inU.S. Pat. No. 5,314,935, which is herein incorporated by referencebeginning in column 7, line 5 through column 8, line 58.

The modified asphalt composition can also comprise other additives knownto those skilled in the art. Additives include nitrogen compounds ofamine or amide which are used as promoters of adhesion for the asphaltand the elastomer.

The modified asphalt compositions can be used to form any suitablearticles. More particularly, the modified asphalt compositions are usedto form road pavement surfaces. To form a road pavement, the modifiedasphalt composition is applied to a surface, such as earth that haspreferably been leveled, using any method, including any method commonlyused in the road paving industry. While the modified asphalt compositionprovides excellent physical characteristics for road pavingapplications, these mixtures may also be used for other constructionpurposes, such as roofing applications.

In another embodiment of this invention, a process is provided toproduce the modified asphalt composition. The process comprisescontacting at least one plastomer, at least one elastomer, asphalt, andoptionally at least one crosslinking agent. The contacting can beconducted by any method known in the art. Generally, the asphalt isheated to its molten state and the plastomer, elastomer, and optionallythe crosslinking agent are then added and mixed into the asphalt toproduce the modified asphalt composition. Preferably, the plastomer andelastomer are added simultaneously. Most preferably, the elastomer,plastomer, and crosslinking agent are added simultaneously.

In another embodiment of this invention, a process for producing a hotmix asphalt composition is provided. The process comprises contacting atleast one plastomer, at least one elastomer, asphalt, aggregate, andoptionally at least one crosslinking agent.

The term “aggregate” is a collective term denoting any mixture of suchmaterials including, but not limited to, sand, gravel, and crushedstone, and the like used with asphalt. The type of aggregate and theamounts used vary depending on the use of the hot mix asphaltcomposition.

In yet another embodiment, a process for producing a modified asphaltcomposition is provided. The process comprises: 1) contacting at leastone plastomer and at least one elastomer in an extruder zone to producea plastomer/elastomer pellet; 2) adding the plastomer/elastomer pelletand optionally at least one crosslinking agent to at least one moltenasphalt to produce a modified asphalt mixture; and e) mixing themodified asphalt mixture in a mixing zone to distribute the plastomer,elastomer, and optionally the crosslinking agent to produce the modifiedasphalt composition. Preferably, the plastomer/elastomer pellet andcrosslinking agent are added simultaneously.

In still another embodiment of this invention, a process for producing amodified asphalt composition is provided. The process comprises: 1)contacting at least one plastomer and at least one elastomer in anextruder zone to produce a plastomer/elastomer pellet; 2) contacting atleast one plastomer and at least one crosslinking agent in an extruderzone to produce a plastomer/crosslinker pellet; 3) adding theplastomer/elastomer pellet and the plastomer/crosslinker pellet to atleast one molten asphalt in a mixing zone to produce a polymer modifiedasphalt mixture; and 4) mixing the modified asphalt mixture in themixing zone to distribute the plastomer, elastomer, and crosslinkingagent to produce the modified asphalt composition. Preferably, theplastomer/elastomer pellet and the plastomer/crosslinker pellet areadded simultaneously.

The extruder zone comprises at least one extruder. The plastomer andelastomer are heated in the extruder zone to a sufficient temperature sothey can be adequately mixed.

The mixing zone comprises any equipment suitable for mixing the asphalt,plastomer, elastomer, and optionally the crosslinking agent. Suitableequipment includes, but are not limited to, low shear mixing equipmentand high shear mixing equipment.

By adding the plastomer, elastomer, and crosslinking agent in pelletform to the molten asphalt, dust and fumes can be significantly reduced.

An advantage of the use of the plastomer is that when the polymers areadded to asphalt, the viscosity of the mixture is only slightlyincreased over the viscosity of asphalt alone. By increasing theviscosity only slightly, the mixture exhibits good hot-mix workabilityand no observable separation. This aids also in the mixing of theelastomer, which is typically very difficult to mix. Furthermore, theplastomers exhibit dispersibility with a large number of asphalts,resulting in mixtures that are storage stable, with no polymer phaseseparation.

The present invention will be more readily understood by reference tothe following examples. There are, of course, many other forms of theinvention which will become obvious to one skilled in the art, once theinvention has been fully disclosed, and it will accordingly berecognized that these examples are given for the purpose of illustrationonly and are not to be construed as limiting the scope of the inventionin any way.

EXAMPLES

Table I lists the test methods used to characterize the modified asphaltcompositions of the examples.

TABLE I Test Name Test Method Performance Graded Asphalt Binders AASHTOMP1 Kinematic Viscosity 135° C. ASTM D 2170 Absolute Viscosity 60° C.ASTM D2171 Toughness and Tenacity ASTM D 5801 Ring and Ball SofteningPoint ASTM D-36 Dynamic Shear Rheometer (DSR) AASHTO TP5 PenetrationASTM D 5 Compatiblity/Separation ASTM D 5976 Elastic Recovery ASTM D6084 Rolling Thin Film Oven Test (RTFO) ASTM D 2872 Pressure AgingVessel ASTM D 6521 Bending Beam Rheometer (BBR) ASTM D 6648 Force RatioAASHTO T-300

One criterion for asphalt performance is the Superpave™ PerformanceGraded (PG) Binder Specification. These parameters, which indicate thevisco-elastic and service performance related properties of asphaltcompositions, were developed to classify materials based uponperformance. The PG parameters measure the properties between the lowtemperature service rating for the material (generally based uponembrittlement cracking) and the high temperature service properties forthe material (generally based upon heat softening) to determine aservice temperature range. The greater the PG temperature range rating,the greater the service range for the material.

Another criterion to evaluate asphalt performance is a group ofhistorical conventional protocols such as Softening Point, Penetration,Force Ratio, Elastic Recovery, Compatibility, Toughness, and Tenacity.These tests assess a variety of physical properties that throughhistorical use and correlation to actual pavement performance are usedto specify an asphalt by various agencies in addition to the Superpavecriteria.

Inventive Examples 1-6, 8-14 and 16 and Comparative Examples 7 and 15 inTables 2 and 3, a PG 64-22 asphalt was modified. The PG 64-22 was heatedto about 370-380° F. to produce a molten asphalt. The Preblend Additives1 and 2 and the Crosslinker Preblend Addtive were added in pellet formto the molten asphalt, and these additives were blended into the asphaltat high shear for about 1 hour followed by paddle agitation (stirring)for two hours at 370-380° F. This procedure was necessary to adequatelyblend the SBS block copolymer into the asphalt in Comparative Examples 7and 15 and Inventive Examples 8 and 16. As can be seen from the data,this 3 hour period of mixing is not necessary when adding preblendedelastomer and plastomer at the same time.

Preblend Additive 1 in Table 2 consisted of a 50/50 by weight blend ofWingflex® 411 SBS block copolymer commercially available from Goodyearand oxidized polyethylene available commercially as Epolene® E-20 waxfrom Eastman Chemical Company. Comparative Example 7 and InventiveExample 8 utilized Kraton® D1184 SBS block copolymer. The CrosslinkerPreblend Additive 1 in Table 2 and Table 3 is 25% by weight sulfur inEpolene® E-20 oxidized polyethylene.

Preblend Additive 2 in Table 3 consisted of a 25/75 by weight blend ofWingflex® 400 SBS block copolymer commercially available from Goodyearand oxidized polyethylene available commercially as Epolene® E-20 waxfrom Eastman Chemical Company. Comparative Example 15 and InventiveExample 16 utilized Kraton® D1184 SBS block copolymer.

The PG Rating and conventional data displayed in Tables 2 and 3indicates the inventive modified asphalt compositions have comparableperformance grades and equivalent or improved conventional properties ascompared to that of an asphalt containing a similar concentration ofelastomer (e.g. SBS block copolymer).

The presence of the plastomer allows a more efficient use of theelastomer in the asphalt to achieve improved properties withoutdetrimental effects such as incompatibility and high process viscositiesassociated with elastomer usage at equivalent dosages.

Comparative Examples 7 and 8

In Examples 7 and 8, modification of the PG 64-22 asphalt with 4%Kraton® D 1184 SBS block copolymer increased the PG grade by 2 grades toa PG 76-22 grade. In Example 8, the addition of a small amount ofcrosslinking agent only slightly increased the performance grade of themodified asphalt. However, the Crosslinker Preblend Additive 1 (Example8) was not added with the Kraton® SBS rubber, but was added after therubber had dissolved. It took the full three hours for the Kraton® SBSrubber to disperse in the PG 64-22 asphalt. It was only after theKraton® SBS rubber had dispersed that the Crosslinker Preblend Additive1 (oxidized polyethylene and sulfur) was added.

Example 7 shows that 4% Kraton® SBS rubber was not very compatible withasphalt in that the softening point after 48 hours at 163° F. was verydifferent at the top (198° F.) and at the bottom (138° F.) of the agedsample. This was not the case for the inventive examples. This is acommon problem with elastomer use and most host asphalts.Incompatibility, also referred to as separation, can typically be causedby a compositional deficiency in the asphalt for elastomer modification.When separation occurs, the ‘dissolved’ polymer phase can separate andrise to the surface of the blend and the asphalt's higher molecularweight component fractions, asphaltenes, can precipitate from theasphalt matrix and sink to the bottom of the blend. This often resultsin process difficulties at a modified asphalt producing facility. Thiscan be followed by process problems at the hot asphalt mix manufacturingfacility, and if incorporated into the pavement structure, pavementsthat under perform. Compatibility is a key property and is incorporatedin nearly all specifications involving asphalt modifiers world wide.

Inventive Examples 1-6 and 9-14

Inventive Examples 1-6 of Table 2 and 9-14 of Table 3 depict thebenefits of modification of asphalt with PreBlend Additives 1 and 2,which are further enhanced by co-use of Crosslinking Preblend Agent 1.These examples, inclusive, displayed separation values of<2° F., asdetermined by the Ring and Ball Softening Point. It should be noted theaddition of Preblend Additives 1 and 2 in pellet form had a significantimproved effect on separation, which may not be realized if thecomponents of the Preblend Additives (oxidized polyethylene and SBSblock copolymer) were added separately. When an asphalt and additivesystem are prone to separation, the asphalt may be remedied through theuse of ancillary technologies such as aromatic oil addition, sourceasphalt blending, use of lower viscosity asphalt, which requires moreelastomer to achieve the desired high temperature requirements. All ofthese processes are costly and time consuming.

Inventive Examples 3 and 5 of Table 1 indicate the benefit of inclusionof the proper dosage of Crosslinking Preblend Agent 1 with PreblendAdditive 1 on Toughness and Tenacity, a measure of the strength understrain of the modified asphalt. These data are compared with InventiveExamples 1 and 2 where sulfur was not used for crosslinking. Toughnessand Tenacity is a parameter used by various State DOTs in their modifiedasphalt specifications to assure the correct type and proper quantity ofelastomer is used to meet the modified asphalt's specified requirements.

Similar improvements are witnessed in the Elastic Recovery properties ofInventive Examples 3 and 5. The elastic recovery (%) ranged from 66-83for the examples involving crosslinking, while Examples 1 and 2 had aelastic recovery ranging from 41-44.

Inventive Examples 1-6 and 9-14 of Tables 2 and 3 display substantiallyreduced process viscosities when compared to Comparative Examples 7 and15 using Kraton® D 1184 alone as a modifier. When using PreblendAdditive 1 containing a 50/50 blend of SBS block copolymer and oxidizedpolyethylene, the viscosities (centistokes) at 135° C. for inventiveexamples 1-6 ranged from 648 to 1,150 centistokes compared tocomparative example 7 where the viscosity was 1,256 centistokes. Whenusing Preblend Additive 2 containing a 25/75 blend of SBS blockcopolymer and oxidized polyethylene, the viscosity of the InventiveExamples 9-14 ranged from 540 to 802 centistokes, while ComparativeExample 15 using only SBS block copolymer as a modifier had a viscosityof 988 centistokes. High process viscosities present problems to thecontractor during mixing of the modified asphalt composition with theaggregates and subsequent compaction of the modified asphalt compositionwith aggregate.

Inventive Examples 2 and 5

Examples 2 and 5 in Table 1 correspond to the Comparative Example 7 andInventive Example 8 in that each contains 96% asphalt. Example 8 is aninventive example, but is used here for comparative purposes to show theadvantage of addition of the elastomer in a pellet with the oxidizedpolyethylene. In addition, Inventive Example 5 and Comparative Example 7both contain 0.5% of Crosslinker Preblend Additive 1. Both of theinventive modified asphalt compositions upgraded the asphalt to the samePG 76-22 grade as the Comparative Example 7 and Inventive Example 8, butat half of the SBS block copolymer level as the comparative modifiedasphalt compositions. In addition, in Inventive Example 5, the PreblendAdditive 1 in pellet form and the Crosslinker Preblend Additive inpellet form were added at the same time as a single blend of pellets.These additives had completely dispersed into the asphalt in 1.5 hourswhich was approximately one half of the time it took the Kraton® SBSblock copolymer to disperse. The compatibility of the modified asphaltcomposition was greatly improved when the inventive additives were used.The Ring and Ball softening point differential on the aged samples after48 hours at 163° F. was only 1 or 2 degrees. Thus, the combination of aplastomer with the elastomer allowed a much more efficient usage of theelastomer in the asphalt matrix which resulted in the same degree ofreinforcement of the asphalt but at half the level of elastomer.

Inventive Example 6

The asphalt was modified by simultaneously adding 4% by weight PreblendAdditive 1 and 1% by weight Crosslinker Preblend Additive 1 with theweight percent based on the weight of the modified asphalt compositionat 370-380° F. and stirring for 1.5 hours. As shown in Table 2, theasphalt PG grade increased by +3 grades to PG 82-22 without the loss oflow temperature properties.

TABLE 2 Data for examples 1 to 8 I-1 I-2 I-3 I-4 I-5 I-6 C-7 I-8Ingredient Specification Weight Percent Asphalt, West Coast 97 96 97 9796 96 96 96 Blend PG 64-22, Preblend Additive 1 3 4 3 3 4 4 — —Crosslinker Preblend 0 0 0.5 1 0.5 1 0 0.5 Additive 1 Kraton ® D 1184SBS — — — — — — 4 4 PROPERTIES: Original Blend Viscosity @ 135° C.,3,000 max. 648 709 721 928 890 1,150 1,256 1,574 cSt Viscosity @ 60° C.P 6,920 10,046 13,409 19,010 33,518 54,703 20,164 29,805 DSR @ 88° C.kPa 1.0 min. — — — — — 0.687 — — (G*/sin d) DSR @ 82° C., kPa — 0.621 —0.986 0.829 1.117 0.764 0.932 (G*/sin d) DSR @ 76° C., kPa 0.935 1.0710.976 1.657 1.361 1.826 1.286 1.519 (G*/sin d) DSR @ 70° C., kPa 1.7161.777 1.655 2.823 2.25 2.768 2.34 2.729 (G*/sin d) Penetration @ °25 C.46 45 42 38 43 40 44 41 dmm Softening Point, ° F. 134.3 137.3 151 162.5170 184 153.5 164.5 Force Ratio @ °4 C., 0.30 min. 0.175 0.194 0.2520.147 0.337 0.283 0.25 0.418 f2/f1 (0.55 cm/min, 24 cm) Toughness &Tenacity @ 25° C. Toughness, in-lbs. 110 min. 117.8 140.8 190.3 135.6232.3 164 199.3 133.8 Tenacity, in-lbs. 75 min. 53 68.7 116.8 49.2 16897.7 128.9 172 Compatibility @ 163° C./48 hrs Top ⅓ Softening 136.5 143142.5 155 164 178 198 167 Point, ° F. Bottom ⅓ Softening 136 144 143 157166 180.8 138 170 Point, ° F. Difference, ° F. 4.0 max. 0.5 1 0.5 2 22.8 60 3 Elastic Recovery, 60 min. 41 44 74 66 83 82 82 90 % @ 25° C.RTFOT Residue Mass Loss, % 0.5 max. 0.229 0.229 0.199 0.142 0.144 0.1140.171 0.142 DSR @ 88° C. kPa 2.2 min. — — — — — 1.245 — — (G*/sin d) DSR@ 82° C. kPa — — — 1.488 1.371 2.289 1.341 1.547 (G*/sin d) DSR @ 76° C.kPa 1.508 2.061 1.577 2.639 2.323 3.854 2.598 2.623 (G*/sin d) DSR @ 70°C. kPa 2.592 3.851 2.904 4.847 4.287 6.05 5.01 4.798 (G*/sin d) ElasticRecovery, 50 min. 54 57 63 53 70 70 73 84 % @ 25° C. PAV Residue (100C., 300 psi, 20 hours) DSR @ 28° C., 5,000 3,923 4,023 3,458 3,972 4,8963,500 3,597 3,973 G*.sin d, kPa DSR @ 25° C., max. 5,677 5,733 5,1075,595 6,929 5,016 5,150 5,684 G*.sin d, kPa BBR @ −12° C., 300 max. 231233 198 240 216 229 210 192 Stiffness, MPa m value 0.300 min. 0.3080.306 0.318 0.308 0.328 0.317 0.307 0.331 BBR @ −18° C., 300 max. 441457 415 485 419 421 401 374 Stiffness, MPa m value 0.300 min. 0.2350.235 0.242 0.235 0.251 0.244 0.236 0.256 Performance Grade 70-22 76-2270-22 76-22 76-22 82-22 76-22 76-22 “True” Performance 75-22 76-22 75-2381-22 80-24 83-23 79-22 81-24 Grade Effective Temperature MP 1 97 98 98103 104 106 101 105 Range, ° C. Grade Change +1 +2 +1 +2 +2 +3 +2 +2Note: I-1 through I-6 and I-8 are inventive examples. C-7 is acomparative example.

Inventive Examples 9-14, and 16

In Inventive examples 9-14 and 16 and Comparative Example 15 of Table 3,a PG 64-22 asphalt was modified by blending the components at high shearfor 1 hour followed by paddle agitation (stirring) for two hours at370-380° F. The procedure was necessary to adequately blend the SBSblock copolymer into the asphalt in example numbers 15 and 16. PreblendAdditive 1 in Table 3 consisted of a 25/75 blend of Wingflex® 400 SBSblock copolymer (Goodyear) and Epolene® E-20 oxidized polyethylene fromEastman Chemical Company. The Comparative Example 15 and InventiveExample 16 utilized Kraton® D1184 SBS rubber. The Crosslinker Additive 1in Table 3 is 25% sulfur in Epolene® E-20 oxidized polyethylene.

Inventive Example 9 and Comparative Example 15 both have 3% by weightmodifier added to the asphalt. It is expected that Comparative Example15 would have greater toughness and tenacity than Inventive Example 9since it contains 3 times the quantity of elastomer. The PreblendAdditive 2 contained a 25/75 blend of SBS block copolymer and oxidizedpolyethylene. It is not expected, however, that both modified asphaltcompositions containing 3% modifier would have almost the exact PG gradefor the modified asphalt composition. As shown in Table 3, the “True”Performance Grade for Inventive Example 9 was 74-21 compared to 75-22for Comparative Example 15. These two examples suggest that theelastomer and plastomer combination allows much more effective use ofthe elastomer to upgrade the asphalt. The plastomer facilitates thedispersal and ordering of the asphalt matrix to more readily takeadvantage of the elastomeric properties imparted to the modified asphaltcomposition.

Inventive Examples 12 and 13 show that at either higher preblendadditive levels or higher crosslinker preblend agent levels furtherimprovement, as evidenced by a higher PG grade of the modified asphaltcomposition, is possible. However, SBS block copolymers tend to begin tohave compatibility issues at these higher loadings

Example # I-9 I-10 I-11 I-12 I-13 I-14 C-15 I-16 Ingredient WeightPercent Asphalt, West Coast 97 96 97 97 96 96 97 97 Blend PG 64-22,Preblend Additive 2 3 4 3 3 4 4 — — Crosslinker Preblend — — 0.5 1 0.5 1— 0.5 Additive 1 Kraton ® D 1184 SBS — — — — — — 3 3 PROPERTIES:Original Blend Spec. Viscosity @ 135° C. 3,000 max. 540 548 609 619 660802 988 1,037 C cSt Viscosity @ 60° C. P 7,027 10,596 10,083 11,04824,556 27,005 6,225 19,905 DSR @ 88° C. kPa — — — — 0.441 0.755 — —(G*/sin d) DSR @ 82° C., kPa — 0.723 — 0.866 1.003 1.378 — 0.677 (G*/sind) DSR @ 76° C., kPa 0.845 1.159 0.983 1.449 1.757 2.113 0.946 1.125(G*/sin d) DSR @ 70° C., kPa 1.0 kPa 1.528 1.993 1.85 1.827 — 3.3571.746 1.937 (G*/sin d) Penetration @ °25 C., 47.3 45.3 44.5 44.1 36 3844 43 dmm Softening Point, ° C. 134.5 143 140 143.5 160.3 170 132 148Force Ratio @ °4 C., 0.300 min 0.113 0.13 0.106 Broke 0.145 Broke 0.2230.375 f2/f1 (5 cm/min, 24 cm) Toughness & Tenacity @ 25° C. Toughness,in-lbs. 110 min. 90.84 93.48 93.81 84.26 110.1 95.85 183.8 265.1Tenacity, in-lbs. 75 min. 26.11 29.29 27.04 15.33 35.26 17.85 102.29191.5 Compatibility @ 163 C./48 hrs Top ⅓ Softening 137 147 140 144.5152.5 161 136 155.5 Point, ° F. Bottom ⅓ Softening 136 147 140 144.5152.5 161.8 135 155.8 Point, ° F. Difference, ° F. 4.0 max 1.0 0.0 0.00.0 0.0 0.8 1.0 0.3 Elastic Recovery, 60 min. 33.5 41 47.3 29.2 57 4347.3 80.5 % @ 25 C. RTFOT Residue Mass Loss, % 0.5 max. 0.057 0.0860.057 0.085 0.072 0.086 0.076 0.056 DSR @ 82° C. kPa — 1.332 — 1.4181.347 1.482 — — (G*/sin d) DSR @ 76° C. 1.601 2.415 2.054 2.517 2.5762.175 1.919 1.901 kPa (G*/sin d) DSR @ 70° C. kPa 2.2 min. 3.23 4.473.749 3.32 — 4.48 3.856 3.53 (G*/sin d) Elastic Recovery, 50 min. 41.547.8 43.8 32 51 36 66 77 % @ 25° C. PAV Residue (100 C., 300 psi, 20hrs) DSR @ 31° C., 3,195 3,023 3,153 3,167 3,190 2,912 2,634 2,074G*.sin d, kPa DSR @ 28° C., 4,447 4,392 4,661 4,605 4,598 4,214 3,8173,104 G*.sin d, kPa DSR @ 25° C., 5,000 max. 5,983 6,260 6,562 6,5046,492 5,946 5,554 4,509 G*.sin d, kPa BBR @ −06° C., 300 max. 117 124117 128 — — — — Stiffness, MPa m Value 0.300 min. 0.344 0.345 0.3430.344 — — — — BBR @ −12° C., 300 max. 260 272 254 274 249 244 211 188Stiffness, MPa m Value 0.300 min. 0.298 0.297 0.302 0.304 0.301 0.3010.309 0.332 BBR @ −18° C., 300 max. 13 — 413 464 413 423 386 381Stiffness, MPa m Value 0.300 min. — — 0.244 0.245 0.246 0.246 0.2480.266 Performance Grade 70-16 76-16 70-22 76-22 76-22 70-22 70-22 70-22“True” Performance M 320 74-21 78-21 75-22 80-22 82-22 84-22 75-22 74-24Grade Effective Temperature 95 99 97 101 104 106 97 101 Range, ° C.

Blending Improvements of Inventive Modified Asphalt Compositions

Table 5 is a mixing time table and shows the progress of the modifiedasphalt compositions of Table 3 while they were blended. A PG 64-22apshalt was modified by blending the components shown in Table 3 at highshear for 1 hour followed by paddle agitation for two hours at 370-380°F. The procedure was necessary to adequately blend the SBS blockcopolymer into the asphalt in Comparative Example 7 and InventiveExample 8. It is clearly shown in Table 5 that the blend times for thePreblend Additive 1 was significantly shortened compared to the SBSblock copolymer addition in Comparative Example 7. The Preblend Additive1 was dissolved in the asphalt in approximately 30 minutes while the SBSblock copolymer took at least 120 minutes to dissolve. This reducedblend time translates into shorter batch times and increased productionrates. Thus, the Preblend Additive of Table 3 is readily soluble inasphalts at useful levels. This solubility also results in reducedtendency for the modifiers to separate upon storage.

TABLE 5 Ingredient −1 −2 −3 −4 −5 −6 −7 −8 Asphalt, West Coast Blend 9796 97 97 96 96 96 96 PG 64-22, Preblend Additive 1 3 4 3 3 4 4 — —Crosslinker Preblend 0 0 0.5 1 0.5 1 0 0.5 additive 1 Kraton SBS D 1184— — — — — — 4 4 Mix/blend: appearance and texture initial, afterCrosslinker Pb A1 addition small Undissolved particles particles present15 minutes nearly all dissolved and dispersed particles present 30minutes smooth and homogeneous nearly dissolved 60 minutes smooth andhomogeneous and dispersed 120 minutes smooth and homogeneous smoothhomogeneous Ease of blending excellent excellent excellent excellentexcellent excellent Good Good Separation/Film formation No Visual DrawDown, undispersed all blends were smooth and homogeneous polymer?

1. A modified asphalt composition produced by the process comprising: 1)contacting at least one plastomer and at least one elastomer to producea pellet; and 2) adding said pellet to asphalt in a mixing zone toproduce said modified asphalt composition. wherein said plastomer isoxidized polyethylene.
 2. A modified asphalt composition according toclaim 1 wherein said oxidized polyethylene has at least one property inthe following ranges: an acid number from about 0.1 to about 50, aneedle penetration hardness less than about 50 dmm at 25° C., and aviscosity from about 1 to about 100,000 cP at 135° C.
 3. A modifiedasphalt composition according to claim 1 wherein said oxidizedpolyethylene is a homopolymer having at least one of the followingproperties: a density from about 0.92 to about 1.1 g/cm³, a hardnessless than about 1.5 dmm at 25° C., an acid number from about 5 to about41, and a viscosity from about 800 to about 8,000 cP at 125° C.
 4. Amodified asphalt composition according to claim 1 wherein said elastomeris a synthetic rubber produced from monomers obtained from the crackingand refining of petroleum.
 5. A modified asphalt composition accordingto claim 4 wherein said monomers are selected from the group consistingof styrene, butadiene, carboxylated butadiene, isobutylene, isoprene,carboxylated isoprene, chloroprene, ethylene, propylene, acrylonitrile,and mixtures thereof.
 6. A modified asphalt composition according toclaim 1 wherein said elastomer is a block copolymer of at least oneconjugated diene and at least one monoalkenyl aromatic hydrocarbon.
 7. Amodified asphalt composition according to claim 6 wherein saidconjugated diene is at least one selected from the group consisting ofbutadiene, isoprene, chloroprene, carboxylated butadiene, andcarboxylated isoprene.
 8. A modified asphalt composition according toclaim 7 wherein said conjugated diene is butadiene and isoprene.
 9. Amodified asphalt composition according to claim 6 wherein saidmonoalkyenyl aromatic hydrocarbon is styrene.
 10. A modified asphaltcomposition according to claim 6 wherein said block copolymer has ageneral formula A-B-A or (A-B)_(n) X; wherein each A block is amonoalkyenyl aromatic hydrocarbon polymer block, each B block is aconjugated diolefin polymer block, X is a coupling agent and n is aninteger from 2 to about
 30. 11. A modified asphalt composition accordingto claim 6 wherein the configuration of said block copolymer is linear,radial, star, or tapered.
 12. A modified asphalt composition accordingto claim 6 wherein said block copolymer has a number average molecularweight from about 30,000 to about 300,000.
 13. A modified asphaltcomposition according to claim 10 wherein said conjugated diene isbutadiene and said monoalkyenyl aromatic hydrocarbon is styrene and theamount of styrene repeating units in said block copolymer ranges fromabout 15% by weight to about 50% by weight based on the weight of saidblock copolymer with the remainder being repeating units derived frombutadiene.
 14. A modified asphalt composition according to claim 6wherein said block copolymer is a styrene-butadiene block copolymerhaving a number average molecular weight ranging from about 50,000 toabout 200,000.
 15. A hot mix asphalt composition comprising saidmodified asphalt composition of claim 1 and aggregate.
 16. A modifiedasphalt composition according to claim 1 wherein the amount of saidelastomer and said plastomer is sufficient to increase the PG rating ofthe modified asphalt composition by +1 to +3 grades.
 17. A modifiedasphalt composition according to claim 1 wherein said plastomer ispresent in said modified asphalt composition in an amount from about0.1% by weight to about 10% by weight based on the weight of themodified asphalt composition.
 18. A modified asphalt compositionaccording to claim 1 wherein said elastomer is present in said modifiedasphalt composition in an amount from about 0.1% by weight to about 10%by weight based on the weight of the modified asphalt composition.
 19. Amodified asphalt composition according to claim 1 wherein said asphalthas a PEN value from about 40 to about 300 dmm.
 20. A modified asphaltcomposition according to claim 1 wherein said asphalt has an AC valuefrom about 2.5 to about 40 hundreds of poises.
 21. A modified asphaltcomposition according to claim 1 wherein said asphalt has an AR valuefrom about 1,000 to about 16,000 poises.
 22. An article produced by themodified asphalt composition of claim
 1. 23. An article produced by thehot mix asphalt composition of claim
 15. 24. A modified asphaltcomposition comprising: at least one plastomer, at least one elastomer,and asphalt, wherein said plastomer is oxidized polyethylene and whereinsaid elastomer is a block copolymer of at least one conjugated diene andat least one monoalkenyl aromatic hydrocarbon.
 25. A process forproducing the modified asphalt composition of claim 24 comprising: 1)contacting at least one plastomer and at least one elastomer to producea pellet; and 2) adding said pellet to asphalt in a mixing zone toproduce said modified asphalt composition.
 26. A modified asphaltcomposition according to claim 24 wherein said conjugated diene is atleast one selected from the group consisting of butadiene, isoprene,chloroprene, carboxylated butadiene, and carboxylated isoprene.
 27. Amodified asphalt composition according to claim 26 wherein saidconjugated diene is butadiene and isoprene.
 28. A modified asphaltcomposition according to claim 24 wherein said monoalkyenyl aromatichydrocarbon is styrene.
 29. A modified asphalt composition according toclaim 24 wherein said block copolymer has a general formula A-B-A or(A-B)_(n) X; wherein each A block is a monoalkyenyl aromatic hydrocarbonpolymer block, each B block is a conjugated diolefin polymer block, X isa coupling agent and n is an integer from 2 to about
 30. 30. A modifiedasphalt composition according to claim 24 wherein the configuration ofsaid block copolymer is linear, radial, star, or tapered.
 31. A modifiedasphalt composition according to claim 24 wherein said block copolymerhas a number average molecular weight from about 30,000 to about300,000.
 32. A modified asphalt composition according to claim 29wherein said conjugated diene is butadiene and said monoalkyenylaromatic hydrocarbon is styrene and the amount of styrene repeatingunits in said block copolymer ranges from about 15% by weight to about50% by weight based on the weight of said block copolymer with theremainder being repeating units derived from butadiene.
 33. A modifiedasphalt composition according to claim 24 wherein said block copolymeris a styrene-butadiene block copolymer having a number average molecularweight ranging from about 50,000 to about 200,000.